The HCV genome is approximately 9.4 kb in length, and encodes at least ten polypeptides. (Kato, Microb. Comp. Genomics, 5:129-151 (2000)). The genomic RNA is translated into one single polyprotein that is subsequently cleaved by viral and cellular proteases to yield the functional polypeptides. (Id.) The polyprotein is cleaved to three structural proteins (core protein, E1 and E2), to p7 of unknown function, and to six non-structural (NS) proteins (NS2, NS3, NS4A/B, NS5A/B). (Id.) NS3 encodes a serine protease that is responsible for some of the proteolytic events required for virus maturation (Kwong et al., Antiviral Res., 41:67-84 (1999)) and NS4A acts as a co-factor for the NS3 protease. (Id.) NS3 further displays NTPase activity, and possesses RNA helicase activity in vitro. (Kwong et al., Curr. Top. Microbiol. Immunol., 242:171-96 (2000)).
HCV infection typically progresses from an acute to a chronic phase. (Virology, Fields ed., third edition, Lippencott-Raven publishers, pp. 1041-47 (1996)). Acute infection is characterized by high viral replication and high viral load in liver tissue and peripheral blood. (Id. at 1041-42.) The acute infection is cleared by the patient's immune defense system in roughly 20-40% of the infected individuals; in the other 60-80% the virus establishes a chronic, persistent infection. (Lawrence, Adv. Intern. Med., 45:65-105 (2000)). During the chronic phase replication takes place in the liver and the virus is readily detected in peripheral blood. (Virology, supra, pp. 1042).
The infected host mounts both a humoral and a cellular immune response against the HCV virus but in most cases the response fails to prevent establishment of the chronic disease. Following the acute phase, the infected patient produces antiviral antibodies including neutralizing antibodies to the envelope proteins E1 and E2. (Id. at 1045). This antibody response is sustained during chronic infection. (Id.) In chronically infected patients, the liver is also infiltrated by both CD8+ and CD4+ lymphocytes. (Id. at 1044-45). Additionally, infected patients produce interferons as an early response to the viral infection. (Id. at 1045). It is likely that the vigor of the initial immune response against the infection determines whether the virus will be cleared or whether the infection will progress to a chronic phase. (Pape et al., J. Viral. Hepat., 6 Supp. 1:36-40 (1999)).
Although a humoral and cellular immune response targeted against the NS3 protein appears to be important in patients who clear an acute HCV infection (see Diepolder H M et al., Lancet, 346(8981):1006-7 (1995) and Missale G., et al., J Clin Invest, 98(3):706-14 (1996)), the HCV proteins that are responsible for inducing an HCV phenotype is largely unknown.
The need for compositions that treat or prevent HCV infection is manifest. This goal is complicated by the fact that the creation of an animal model for HCV infection has proven difficult. So far, human, chimpanzees, and tree shrews are the primary animals that are susceptible for infection with human HCV (Xie et al. Virology 244:513-20 (1998)). HCV has been reported to infect primary cultures of human hepatocytes; however, the cells do not support the production of progeny virons (Fournier et al. J Gen Virol 79 (Pt 10):2367-74 (1998)). Current animal models either do not exhibit the normal course of infection or require the use of previously infected human liver cells, or both. (See, e.g., WO 99/16307; Galun et al. J. Infect. Dis. 172:25-30 (1995); Bronowicki et al. Hepatology 28:211-8 (1998); and Lerta et al. Hepatology 28 (4Pt2):498A (1998). Two exceptions to this are that Chimpanzees and uPA-Scid mice repopulated with human liver can both be infected in vivo (Mercer et al., Hepatitis C virus replication in mice with chimeric human livers. Nat. Med., 7(8):927-33 (2001)).
One recent attempt to overcome these obstacles was described in U.S. Pat. No. 6,509,514, issued Jan. 21, 2003 to Kneteman et al., herein expressly incorporated by reference in its entirety; however, the production of Kneteman's modified mouse required engrafting human hepatocytes into a mouse liver, a time consuming and laborious process. Another drawback of this approach is that the mice were found to be immunocompromised.
Another attempt to overcome these obstacles was described in U.S. Pat. No. 6,201,166, issued Mar. 13, 2001 to Kohara et al. (involving the use of a Cre-loxP switch system to attempt to drive expression of particular HCV proteins), herein expressly incorporated by reference in its entirety. Kohara et al., however, only expressed certain types of HCV proteins (CN2, N24 or CR) and the approach required activation of the Cre-loxP system in order to induce HCV protein expression. There remains a need for more transgenic models of HCV infection and compositions that treat or prevent HCV infection.